Conventionally, liquid crystal monitors for displaying video signals, given from an external device, on liquid crystal screens have been frequently used as video display devices.
Generally speaking, liquid crystal monitors are driven based on power, supplied from external power sources, which is needed to perform image processing on video input signals supplied from external devices and to display images on display screens.
FIG. 3 is a diagram showing the configuration of a conventional liquid crystal monitor 110. For example, the liquid crystal monitor 110 includes a power circuit 305, a power supply block A 302, a power supply block B 303, and a liquid crystal panel 4.
The power circuit 305 includes power output circuits 306 and 307. The power output circuit 306 converts an AC voltage (e.g. 100 V to 240 V), which is supplied from an outlet socket via a socket plug 201 and an AC (Alternating Current) power supply line 300, into a DC (Direct Current) voltage, which is supplied to the power supply block B 303, e.g. a DC voltage of 19 V, thus supplying it to the power supply block B 303. Additionally, the power output circuit 307 converts the foregoing AC voltage into a DC voltage which can be supplied to the power supply block A 302, e.g. a DC voltage having a value of 5 V, thus supplying it to the power supply block A 302.
The power supply block A 302 includes a DC/DC converter 18, a CPU circuitry 11, a video processing circuit 12, and a liquid crystal display control circuit 13.
The DC/DC converter 18 transforms or reduces a DC voltage of 5 V, which is supplied from the power output circuit 307, so as to generate another DC voltage, e.g. a DC voltage of 1.9 V, thus supplying the generated DC voltage of 1.9 V to the CPU (Central Processing Unit) circuitry 11 via the DC power supply line 207. The CPU circuitry 11 has a plurality of semiconductor chips, each of which includes a chip set having a CPU and a memory and each of which operates based on a driving voltage of 1.9 V.
Additionally, the DC/DC converter 18, the video processing circuit 12, and the liquid crystal display control circuit 13 are each supplied with a DC voltage of 5 V from the power output circuit 307. Similarly, the CPU circuitry 11 is supplied with a DC voltage of 5 V from the power output circuit 307.
The video processing circuit 12 performs image processing, for displaying images on the liquid crystal panel 4, on video input signals, which are supplied from an external device via a video input signal line 101, based on a video control signal which is supplied from the CPU circuitry 11 via a control signal line 209. Subsequently, the video processing circuit 12 outputs video data, going through image processing, to the liquid crystal display circuit 13 via a video signal line 210.
The liquid crystal control circuit 13 controls the liquid crystal display device 15, arranged inside the liquid crystal panel 4, based on video data supplied thereto via a liquid crystal display control line 213 while supplying a DC voltage of 5 V to the liquid crystal display device 15 via a power supply line 214. The liquid crystal display device 15 displays images, based on video data supplied thereto, by controlling liquid crystal elements.
The power supply block B 303 includes a backlight control device 14. The backlight control device 14 is supplied with a DC voltage of 19 V from the power output circuit 306 via a DC power supply line 308 and supplied with a backlight control signal via a backlight control signal line 208.
The backlight control device 14 includes a voltage conversion circuit (e.g. a DC/DC converter) therein and boosts a DC voltage of 19 V supplied thereto to a voltage ranging from 40 V to 50 V so as to supply a DC voltage of 40 V to the backlight 16 as a driving voltage via a backlight power supply line 212 while controlling the backlight 16 based on a backlight control signal input thereto via a backlight control output signal line 211.
That is, the liquid crystal monitor converts an externally supplied voltage into a DC voltage whose value is needed to drive each of internal circuit blocks by way of the internal power circuit thereof (see Patent Literature 1).
In the liquid crystal monitor of FIG. 3, for example, a power circuit generates a plurality of DC voltages used for various circuits of the liquid crystal monitor, based on an AC voltage supplied thereto via the socket plug 201 and the AC power supply line 300, thus supplying them to various circuits.
When an external battery is provided to supply a DC voltage used for each internal circuit, however, it is necessary to supply a plurality of DC voltages used for various internal circuits. For this reason, a conventional liquid crystal monitor needs to install a plurality of batteries therein; hence, a conventional liquid crystal monitor has a drawback in that it cannot be used for a display device for a portable device because the weight thereof may increase by installing a plurality of batteries therein.